Resonant combustor with spiral exhaust passageways



April 28, 1970 5 sl ET AL 3,508,398

RESONANT COMBUSTOR WITH SPIRAL EXHAUST PASSAGEWAYS Filed March 25, 1968 2 Sheets-Sheet 1 ATTORNEY April 28, 1970 RSSIEGLE ETAL 3,508,398

RESONANT COMBUSTOR WITH SPIRAL EXHAUST PASSAGEWAYS Filed March 25, 1968 2 Sheets-Sheet 2 INVENTORS.

ROBERT 5. 5/564 ER ROBERT 4. swvsz. EV

BYEUGENE 8. zn/zc/r 3,508,398 RESONANT COMBUS'IOR WITH SPIRAL EXHAUST PASSAGEWAYS Robert S. Siegler, Hidden Hills, Robert L. Binsley,

Sepulveda, and Eugene B. Zwick, Northridge,

Calif., assignors to North American Rockwell Corporation Filed Mar. 25, 1968, Ser. No. 715,820 Int. Cl. F02c 5/10 US. Cl. 6039.77 11 'Claims ABSTRACT OF THE DISCLOSURE A pulse jet-type or resonating combustor having an annular space incorporating a plurality of laterally spaced, spirally oriented vanes. Adjacent vanes and the walls defining the annular space form spiral exhaust passageways. The axial length of the combustion chamber-combined with the longitudinal spiral length of an exhaust passageway equals the acoustical length for achieving resonant combustion. The configuration of the exhaust passageways allows the end to end length of the combustor to be shorter than the overall acoustical length.

BACKGROUND OF THE INVENTION The present invention relates to a pulse jet-type or resonating combustor whose combustion gases are discharged through spirally oriented exhaust passageways to a turbine designed to start the operation of a self-sustain ing engine.

The broad concept of positioning the exhaust exit of a pulse jet-type combustor in operative driving relationship with a turbine is known in the art. Such a power generating arrangement used as a supercharger for a vehicle internal combustion engine is disclosed in U.S. Patent 2,963,863 to Middlebrooks. It is also known in the art to use the hot gases generated in a combustor, not of the pulse jet-type, for operating a turbine designed to start, i.e., initiate the motion of, an engine system (e.g., US. Patent 3,004,387 to Woodwar.

It is known to drive turbines with combustion gases from an internal combustion engine whose combustion chamber and single exhaust passageway are shaped into a reverse bend annular path (e.g., US. Patent 1,278,499 to Esnault-Pelterie). Another related approach for driving a starter turbine with combustion gases guided over a tortuous, zig-zag path is disclosed in US. Patent 2,908,135 to King et al. Conventional combustors of this type, none of which are resonating or pulse jet-type combustors, have their combustion chambers and exhaust passageways specially shaped so as to conserve space, weight, etc. or to assure that suflicient space is'provided to assure complete decomposition of the combustion ingredients. Combustion chambers and exhaust passageways of these conventional combustors are not shaped to constitute an acoustical length which is crucial to the performance of resonating combustors as shall be more fully described.

As disclosed in co-pending U.S. applications, Ser. No. 576,726, filed Sept. 1, 1966 now Patent No. 3,411,292, and Ser. No. 583,624, filed Oct. 3, 1966 now abandoned (which applications are assigned to the assignee of this invention) the combustion product of a resonating or pulse jet-type combustor can be discharged through a plurality of exhaust passageways onto the blades of starter turbine designed to initiate the operation of a self-sustaining engine. This invention is concerned with positioning one or more spirally oriented exhaust passageways constituted in part by laterally spaced vanes within an annular space so as to diminish the end to end combustor length.

United States Patent 0 SUMMARY OF THE INVENTION Briefly described, the present invention comprehends a resonant combustor having a tubular casing, one section of which partially forms the combustion chamber. A deflector plate of cylindrically shape is positioned Within and radially spaced from a rearward section of the casing. The casing section that partially forms the cornbustion chamber mounts a conventional air inlet, fuel inlet and an igniter for igniting mixtures of air and fuel to generate combustion product. A convexly contoured forward wall portion of the deflector plate in cooperation with casing, defines the combustion chamber. The cylindrical wall portion of the deflector plate and the rearward portion of the casing defines an annular space. A plurality of laterally spaced spirally oriented vanes are positioned within the annular space to define spiral exhaust passage ways. The radially inner edges and the radially outer edges of the major segments of the vanes are attached in fluid tight engagement with the deflector plate and easing, respectively. The vanes are preferably coextensive so that exhaust passageways of equal length are formed. The radially inner edges of the forward ends of the vanes are attached to the forward deflector wall such that the vane ends mutually intersect to form exhaust passageway entrances. The entrances shaped by the vanes and convexly contoured Wall serve to divide the combustion product into segments and guide the segments into the plural passageways. The passageway entrances may be of equal size and the entire annular space may be occupied by exhaust passages. The radially outer edges of the forward vane ends diverge rearwardly toward the exhaust exits and are secured in flush fluid-tight relationship with a complementary shaped conical section of the casing. The combined axial length of the combustion chamber and longitudinal spiral length of an exhaust passageway is equivalent to the requisite acoustic-a1 length for assuring resonant and self-sustaining combustion. By arranging the exhaust passageways in spiral configurations the overall end to end length of the combustor is made shorter than that of a conventional resonant combustor capable of generating equivalent thrust.

BRIEF DESCRIPTION THE DRAWINGS The advantages and unique aspects of the present invention will be fully understood when the following detailed description is studied and in conjunction with the detailed drawings in which:

FIG. 1 is a schematic sectional view taken along the longitudinal axis of the resonant combustor and adjacent starter turbine, showing a plurality of vanes that define spiral exhaust passageways;

FIG. 2 is a side view showing a plurality of spirally oriented vanes attached to a deflector wall and two reduced-size casing sections exploded away from the vanes and deflector w-all component;

FIG. 3 is a view of the forward or upstream end of the vanes-deflector wall component, showing how the vanes form plural exhaust passageway entrances; and,

FIG. 4 is a view of the rearward or downstream end of the vanes-deflector wall component, showing how the exhaust passageways terminate in multiple arcuate exits.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings for a full description of the advantages and unique aspects of the present invention, FIG. 1 schematically illustrates a pulse jet-type or resonating combustor 10* designed to discharge combustion product on the blades 12 of a turbine 13 connected to a power shaft 14. Combustor 10 incorporates a bank of air inlet flapper valves whose inner ends terminate in a plane 22 that perpendicularly intersects combustor axis 23. A suitable type of flapper valve system is disclosed in previously mentioned U.S. application, Ser. No. 576,726. Charges of air admitted through flapper valves 20 are mixed with fuel introduced from injectors 25 incorporated within a combustion chamber 27. The desired air and fuel mixture is ignited by a spark plug 28. The space occupied by combustion chamber 27 is defined by the inner surfaces of flapper valves 20, a forwardly extending section of a tubular casing 30 and an end wall 32 of a deflector wall plate. The rearward ends of outer casing 30 and deflector plate 33 lie within an exhaust exit plane '35. The rearward section of casing 30 surrounds and is radially displaced from a cylindrical wall portion 36 of deflector plate 33. Casing 30 and cylindrical wall 36 coact to define an annular space 38 arranged with its forward end 41 in fluid communication with combustion chamber 27 and its rearward end 42 terminating at exit plane 35. Arranged within annular space 38 is a plurality of laterally spaced, spirally oriented vanes 45. The radially outer edges 46 of vanes 45 are secured to outer casing 30 while the radially inner edges 47 are secured to cylindrical wall 36. Combustion product is divided into separate streams and passed through spirally oriented passageways 49 defined between adjacent vanes 45. Eventually the streams are ejected from passageways 49 and impinge on turbine blades 12.

Before describing further structural details of resonant combustor 10 it would prove beneficial to describe a basic resonant combustion cycle. Unlike other types of combustors, resonant combustors must be sized and shaped to possess a particular acoustical length, the accuracy of which vitally affects the operation and efficiency of the combustor. In the case of conventional valved pulse-jet combustors the acoustical length is equivalent to the overall end-to-end length of the combustor. This necessitates excessive length, weight, cost, space consumption, etc., which disadvantages are overcome by the present invention. In combustor 10 the acoustical length is constituted by the longitudinal length of a spiral passageway 49' plus the axial length of combustion chamber 27. Thus the acoustical length is larger than overall combustor length 'L. By this arrangement combustor 10 is shorter, lighter, and consumes less envelope volume than conventional resonant combustors capable of generating equivalent power. When the combined length of the combustion chamber 27 and a spiral exhaust passageway 49 (which functions like a tailpipe of conventional pulse jet-type combustors) is less than the minimum acoustical length, then, after the initial explosion the combustor would fail to resonate and its operation would terminate. When the combined length of combustion chamber 27 and a spiral passageway 49 becomes greater than the acoustical length then combustion efliciency and thrust correspondingly diminish. The proper acoustical length can be approximately calculated from formulas, but is ultimately ascertained empirically. To begin the combustion cycle, air and fuel are mixed and ignited causing an explosion that transmits a pressure wave (i.e., a wave that compresses fluid such that the pressure at a given point increases when the wave has passed) from combustion chamber 27 through spiral passageways 49 and eventually beyond exit plane 35. A second wave in the form of an expansion wave (i.e., a wave that expands or rarefies fluid such that the pressure at a given point is diminished after the wave has passed) is then reflected from exit plane and moves in a reverse direction to air inlet plane 22. The presence of the expansion wave within combustion chamber 27 causes the pressure within chamber 27 to diminish below ambient pressure. Differential pressure causes fresh charges of air to be drawn through flapper valves 20. A third wave in the form of a second expansion wave then travels through spiral passageways 49 and out exit plane 35. A charge of backflow air driven by a fourth wave in the form of a pressure wave then enters spiral passageways 49 and eventually rams and precompresses the fuel and air mixture in combustion chamber 27. Another explosion initiates a second cycle. Each resonant combustion cycle is characterized by four trips of pressure and expansion waves over the acoustical length of combustor 10. Combustor 10 becomes self-sufiicient and the explosions are repeated automatically until terminated by some external force.

FIG. 2 shows three basic resonant combustor components, two of which are reduced in size and exploded away from the other one. Spirally wound around the external periphery of a cylindrically shaped, preferably hollow deflector plate 50 are a plurality of vanes 52, four of which are shown. The radially inner edges 55 of vanes 52 are secured in fluid-tight relationship to plate 50. The forward end 53 of the deflector plate 50 is convexly contoured for mounting the radially inner edges of the forward vane ends 54. FIG. 3 shows that the forward vane ends 54 mutually intersect to form four equally sized exhaust passageway entrances 56. Vane ends 54 and convexly contoured wall 53 divide the combustion product into four streams that are smoothly deflected into the exhaust passageways 57. Ends 54 and wall 53 coact such that the separate streams of combustion product are drawn into their respective exhaust entrances 56 with minimum turbulence. As shown in FIG. 4, vanes 52 terminate so as to form exhaust exit openings 59 of arcuate shape. The deflector wall and vanes are sized to be assembled within a tubular casing section 61 (shown in reduced size) 'whose overall length between its exit end 62 and entrance end 63 is approximately equivalent to the length of deflector plate 50. Forward end 63 is sized for connection to end 65 of another casing section 66. A tubular portion 67 serves as a combustion chamber wall portion. The radial upper edges 69 of vane ends 54 diverge rearwardly and are shaped to be attached in fluid-tight relationship with a complementary conical section 68 of casing section 66. When the combustor is assembled, the radially inner and outer edges of vanes 52 are attached in fluid-tight relationship with the deflector wall and casing respectively.

It can now be understood how the annular space and spirally aligned exhaust passageways coact to achieve the necessary acoustical length while allowing the overall end-to-end combustor length to be decreased.

Although numerous combustors of various sizes and dimensions can be assembled, one that has been built and successfully operated had a combustion chamber diameter of 4", a maximum Casing diameter of 6%, an overall end-to-end combustor length of 23" and an acoustical length of 46".

What is claimed is:

1. In a resonant combustor having a tubular casing, a combustion chamber within the casing, an air inlet positioned within the casing, a fuel inlet positioned within the casing, and means for igniting mixtures of air and fuel to generate combustion product, the improvement comprising;

a deflector plate positioned within the casing, the deflector plate and casing defining an annular space, and

means within the annular space defining an elongated spirally oriented exhaust passageway disposed along and secured within the longitudinal length of said annular space in fluid communication with the combustion chamber at its forward end and which terminates at its rearward end in an exhaust exit, the combined axial length of the combustion chamber and longitudinal length of the spiral exhaust passageway being equivalent to the acoustical length for achieving resonant combustion.

2. The combustor according to claim 1 wherein the exhaust passageway is defined by laterally spaced, spirally oriented fixed vanes.

3. In a resonant combustor having a tubular casing, a combustion chamber within the casing, an air inlet positioned within the casing, a fuel inlet positioned within the casing, and means for igniting mixtures of air and fuel to generate combustion product, the improvement comprising;

a deflector plate positioned within the casing, the deflector plate and casing defining an annular space, and means within the annular space defining a spirally oriented exhaust passageway wherein the exhaust passageway is defined by laterally spaced, spirally oriented vanes, the radially inner and outer edges of the vanes being secured in fluid-tight relationship to the deflector wall and casing respectively, said passageway being in fluid communication with the combustion chamber at its forward end and which terminates at its rearward end in an exhaust, the combined axial length of the combustion chamber and longitudinal length of the spiral exhaust passageway being equivalent to the acoustical length for achieving resonant combustion.

4. The combustor according to claim 3 wherein said deflector plate is of cylindrical shape and has a convexly contoured forward wall portion that forms a portion of the combustion chamber, and

the inner edges of forward vane ends are secured to said forward wall portion. 5. The structure according to claim 1 wherein a plurality of exhaust passageways are positioned within the annular space and are defined by a plurality of laterally spaced, spirally oriented fixed vanes.

6. In a resonant combustor having a tubular casing, a combustion chamber within the casing, an air inlet positioned within the casing, a fuel inlet positioned within the casing, and means for igniting mixtures of air and fuel to generate combustion product, the improvement comprising:

a deflector plate positioned within the casing, the deflector plate and casing defining an annular space, and

means within the annular space defining a plurality of spirally oriented exhaust passageways wherein the exhaust passageways are defined by a plurality of laterally spaced, spirally oriented vanes, said passageways being in fluid communication with the combustion chamber at their forward ends and which terminate at their rearward ends in arcuate exhaust exits aligned adjacent the blades of a turbine, the combined axial length of the combustion chamber and longitudinal length of the spiral exhaust passageways being equivalent to the acoustical length for achieving resonant combustion.

7. A resonant combustor comprising,

a tubular casing,

a combustion chamber partially formed by one section of the casing,

an air inlet positioned within the casing,

a fuel inlet positioned within the casing,

means for igniting mixtures of air and fuel to generate combustion product,

a cylindrically shaped deflector plate positioned within a second section of the casing, the deflector wall and casing defining an annular space,

a convexly contoured forward wall portion of the degector plate that forms part of the combustion chama plurality of laterally spaced spirally oriented vanes positioned within the annular space, adjacent vanes of which define exhaust passageways in fluid communications with the combustion chamber at their forward ends and which terminate at their rearward ends in exhaust exits,

wherein the radially inner and outer edges of the vanes are secured in fluid-tight relationship to the deflector wall and easing respectively and the inner edges of the forward vane ends are secured to the convexly contoured wall, and, the combined axial length of the combustion chamber and longitudinal length of a spiral exhaust passageway is equivalent to the acoustical length for achieving resonant combustion.

8. The combustor according to claim 7 wherein the vane forward ends mutually intersect to form exhaust passageway entrances that divide the combustion product into segments and guide them into the passageways.

9. The structure according to claim 8 wherein the exhaust exits are arcuate and aligned adjacent the blades of a turbine.

10. The combustor according to claim 8 wherein the vanes intersect such that the passageway entrances are of equal size and the entire annular space is occupied by exhaust passageways.

11. The combustor according to claim 8 wherein the radially outer edges of the vane forward ends diverge rearwardly and are secured to a complementrary shaped conical section of the casing.

References Cited UNITED STATES PATENTS 1,246,159 11/1917 Ricardo et al -32 3,258,919 7/1966 Klein 6039.77 3,264,824 8/1966 Bost 60-247 XR FOREIGN PATENTS 801,040 9/ 1958 Great Britain. 928,866 6/ 1947 France.

CARLTON R. CROYLE, Primary Examiner D. HART, Assistant Examiner 

